Systems and methods for illuminating a platen in a print scanner

ABSTRACT

Systems and methods for illuminating a platen are provided. A hybrid illumination system uses both diffusion and collimation to efficiently provide a flat, uniform illumination at a platen. One or more diffusers are disposed between the illumination source array and a collimating lens. An illumination system is provided which uses diffused light to illuminate a platen in a print scanner. The illumination system has an illumination source array and a light wedge. The light wedge reflects light internally which makes the illumination even more diffuse. An illumination source array has a plurality of sources that emit blue/green light. In one preferred example, the blue/green light is equal to or approximately equal to 510 nm. Sources are divided into at least a center region and a perimeter region. The density of sources provided in the perimeter region is greater than in the center region to correct for natural light falloff in the illumination system. Intensity control can be preformed individually or in groups.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to biometric imaging technology, and inparticular, to live scanning of fingerprints and/or palm prints.

2. Background Art

Biometric imaging systems may include, but are not limited to,fingerprint imaging systems and palm print imaging systems. Such printimaging systems are also referred to as scanners or live scanners.Conventional live scanners use light to detect an image of a fingerprintand/or palm print. One or more fingers or palms are placed on a platen.An illumination source illuminates the underside of the platen. An imagerepresentative of valleys, ridges, or other characteristics of afingerprint or a palm print is then detected by an image sensor, suchas, a solid-state camera.

The illumination source must have sufficient power so that a highquality image representative of a print is detected by the image sensor.Often the optical system employed in a print scanner is telecentricwhich further increases the power required at the illumination source.In a telecentric system an aperture is used to limit light passingthrough the optical system. In this way, only light rays travelingwithin a range of angles at or near a direction along an optical axisare detected. Such telecentricity improves the image quality and reducesblurring, but has a drawback in that increased power is required at theillumination source to ensure that sufficient light passes through theaperture of the optical system to the image sensor.

Collimated light has been used in an illumination source for a printscanner to reduce the power required. A collimated lens collimatesincoming light rays so that collimated light rays exit which travelparallel to one another. Because the rays are made parallel they travelefficiently through a telecentric optical system. FIG. 1A shows anexample of a collimated light source lighting technique. A singlediscrete light source 110 emits light over an area as indicated byexample rays 112. The actual emission area depends upon the type ofemitter and other factors such as whether a lens, light guide or otheroptical element is provided to focus or guide the emitted light. Asubset 115 of rays 112 are collimated by collimating lens 120 and emergeas parallel rays 125. The subset rays 115 are those rays within anangular range A at the focal point of collimating lens 120 as shown inFIG. 1A.

Collimated illumination source lighting techniques provide a relativelyefficient, low power source especially in a telecentric optical system,but lack sufficient good grey scale shading for uses in high-qualityfingerprint and/or palm print scanners. FIG. 1B shows an exampleconventional fingerprint or palm print scanner using collimatedillumination in a telecentric optical system. A single discrete lightsource 110 emits red light which is collimated by collimating lens 120before illuminating a prism 130. In this case, a top surface of prism130 serves as a platen. The collimated light illuminates the undersideof prism 130. When one or more fingers or palms are placed on prism 130,an image representative of valleys, ridges, and other characteristics ofa fingerprint or a palm print is then focused by imaging lens 140 toaperture 150, and then further focused by imaging lens 160 to a focalplane/sensor plane 170. One or more image sensors, such as, solid-statecameras (CCD or CMOS cameras) detect the image. The use of collimatedlight improves the efficiency in which light travels through thetelecentric optical system from the collimating lens 120 to the prism130 and eventually through aperture 150 to an image sensor at focalplane/sensor plane 170.

While the collimated light is efficient, such illumination can produceprint images having limited or no grey scale shading because the lightrays incident on a platen are generally parallel. Such parallel rays arethen either reflected or absorbed by a biometric object, such as, afinger or palm ridge. This tends to create a high contrast print havingessentially black and white values only and no grey shade values. Suchhigh contrast prints (also called binary prints) do not provide the fullspectrum of grey shades required for many applications such as,forensics, law enforcement, security, and anti-terrorism. This canresult in unacceptable images being captured especially in cases wheresignificant pressure is placed on a finger or palm during the live scan.

As an alternative to collimated lighting techniques, print scanners haveused diffuse source lighting. Diffuse light includes rays traveling inmany different directions which tends to provide a flat, uniformillumination with good fill. In a print scanner, such diffuse lightallows good grey scale shades to be detected since light traveling in anumber of different directions is incident on a platen. One disadvantageis the illumination power required is high, especially in a printscanner having a telecentric optical system. The high power requiredmeans more light sources need to be used which, among other things,increases cost and the amount of heat generated.

FIG. 2 shows an example print scanner using a diffuse light source 205that illuminates prism 130. Diffuse light source 205 includes a discreteemitter array 210 and a diffuser 220. Discrete emitter array 210 is madeup a number of evenly spaced light emitting diodes that emit red light.As shown schematically in FIG. 2, diffuse light source 205 is aninefficient light source for generating an image and passing the imageto an image sensor in a telecentric system. Diffuse light travelsrandomly or in different directions and is not transmitted through anentire telecentric system. For instance, much of the light is blocked byaperture 150. Such inefficiency in illumination of a print scanner isundesirable as it increases the number of emitters needed in array 210and the power requirements of array 210. This problem is even more acutefor telecentric print scanners where flat, uniform illumination isneeded across a relatively large platen, such as, a platen big enough toallow capture of images for a roll print or slap print of one or morefingers, or a palm print.

In sum, the above drawbacks of using either collimation or diffuseillumination approaches in a print scanner need to be overcome. Otherneeds also exist in print scanner illumination. These needs include: aneed for improved diffuse illumination of a print scanner, a need forproviding a greater dynamic range of grey shading output from a camera,and a need for providing more uniform illumination from an illuminationsource array with flexible control.

BRIEF SUMMARY OF THE INVENTION

The present invention provides systems and methods for illuminating aplaten. The present invention, among other things, overcomes the abovedrawbacks and meets the above needs. Four techniques for improving printscanner illumination are provided. The first technique involves hybridillumination systems and methods that use both diffusion andcollimation. The second technique involves diffuse light illuminationsystems and methods that use a light wedge. The third technique involvesuse of a non-uniform illumination source array and use of independentand/or zone controlled light sources. The fourth technique involves useof blue/green light. Each of these techniques can be used alone or indifferent combinations as described herein with respect to embodimentsof the present invention.

According to one embodiment of the present invention, a hybridillumination system provides illumination to a platen in a printscanner. The hybrid illumination system uses both diffusion andcollimation to efficiently provide a flat, uniform illumination at aplaten. An illumination source array emits light from a plurality ofdiscrete light sources. One or more diffusers are disposed between theillumination source array and a collimating lens. At least part of thelight emitted from the plurality of discrete light sources passesthrough at least one diffuser and then through a collimating lens. Eachdiffuser serves to randomize light so that a flat, uniform illuminationis obtained at the platen. The individual cones of light initiallyemitted from the discrete sources are no longer visible. The collimatinglens increases the efficiency of the illumination system and reduces thepower requirements of the illumination source array. Fewer light sourcesare needed. This efficiency is especially advantageous in a telecentricoptical system of a print scanner.

In one embodiment, the hybrid illumination system has one diffuser. Thediffuser is provided near the collimating lens. Alternatively, thediffuser can be provided near the illumination source array or at anyother location between the illumination source array and collimatinglens depending upon a particular design.

In another embodiment, the hybrid illumination system has two diffusers.One diffuser is provided near the illumination source array and theother diffuser is provided near the collimating lens. In one example,two holographic diffusers are used. In another example, a holographicdiffuser is provided near the collimating lens while a cheaper glass orplastic diffuser is provided near the illumination source array. Instill another example, a glass or plastic diffuser is provided near thecollimating lens and a glass or plastic diffuser is provided near theillumination source array.

The examples are illustrative and not intended to limit the presentinvention. Any type of diffuser can be used including, but not limitedto, a glass type diffuser, plastic type diffuser, or a holographicdiffuser. In general, holographic diffusers are more efficient but arealso more expensive than glass or plastic diffusers.

According to a further embodiment, an illumination system is providedwhich uses diffuse light to illuminate a platen in a print scanner. Theillumination system has an illumination source array and a light wedge.The light wedge reflects light internally which makes the illuminationeven more diffuse. The light wedge has one end surface that receiveslight emitted from the illumination source array. The light wedge alsohas a reflective surface that reflects light out of the light wedgetoward the platen. The reflective surface can be any type of reflectivesurface. In one example, a reflective layer of paint such as white, goldor silver paint is applied to the wedge surface. According to a furtherfeature, the wedge reflective surface is roughened and a reflectivepaint layer is applied. Light incident on the wedge is diffuse,reflective surface is then made even more diffuse. In one embodiment, adiffuser is also provided near the light wedge such that light passesout from the light wedge to the diffuser before illuminating the platen.

According to a further feature of the present invention, an illuminationsource array is made up of a plurality of sources divided into at leasta center region and a perimeter region. The density of sources providedin the perimeter region is greater than in the center region to correctfor natural light falloff in the illumination system. In anotherembodiment, the illumination source array is made up of a plurality ofsources divided into at least a center region, one or more intermediateregions, and a perimeter region. The density of each region isprogressively higher toward the perimeter to correct for natural lightfalloff in the illumination system. The density of sources provided inthe perimeter region is greatest and the density of sources provided inthe center region is least. The density of sources provided in eachintermediate region is in between that of the perimeter and centerregions.

According to a further feature of the present invention, the intensityof each source of an illumination source array can be independentlycontrolled relative to other sources. For example, each source can be alight emitting diode which is individually current controlled to correctfor or minimize drift and to ensure a flat, uniform illumination isprovided to a platen.

According to a further feature of the present invention, theillumination source array is divided into zones. In one embodiment, aplurality of sources are divided into at least three groups in at leastthree respective zones. The intensity of each group of sources isindependently controlled relative to other groups such that a flat,uniform illumination is provided to the platen. Use of such zonessimplifies control while still retaining sufficient flexibility toadjust the relative intensity of the light source groups to ensure flat,uniform illumination is provided to a platen.

According to a further feature of the present invention, an illuminationsource array comprises a plurality of sources that emit blue/greenlight. In one preferred example, the blue/green light is equal to orapproximately equal to 510 nm. A method includes the steps of emittingblue/green light from a plurality of discrete sources, and illuminatinga platen with at least part of the emitted blue/green light. Compared toconventional red light operating at 650 nm, the inventors found thatblue/green light increases the dynamic range of grey scale shading in animage of a print of a finger or palm detected with a print scanner.

According to another embodiment, a method provides flat, uniformillumination efficiently to a platen. The method includes the steps ofemitting light from a plurality of discrete sources, randomizing theemitted light to obtain diffuse light, collimating at least part of thediffuse light, and illuminating the platen such that an image of a printof a finger or palm placed on the platen can be obtained. Therandomizing step can include passing the emitted light through at leastone diffuser or through a light wedge. In one example, the emitting stepincludes emitting blue/green light.

Prior to the emitting step, an arranging step includes arranging theplurality of discrete sources into at least a center region and aperimeter region wherein the density of sources provided in theperimeter region is greater than in the center region. Another stepwhich can be performed is independently controlling the intensity ofeach source relative to other sources such that a flat, uniformillumination is provided to the platen.

According to a further embodiment, a system for providing flat, uniformillumination efficiently to a platen includes means for emitting light,means for randomizing at least part of the emitted light to obtaindiffuse light, and means for collimating at least part of the diffuselight. In this way, a portion of the diffuse light is collimated andfalls on the platen as collimated light, while remaining diffuse lightfalls on the platen as diffuse light. The platen is illuminated withthis collimated, diffuse light such that a high contrast image of aprint of a finger or palm placed on the platen is obtained.

Further embodiments, features, and advantages of the present inventions,as well as the structure and operation of the various embodiments of thepresent invention, are described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the pertinent art to makeand use the invention. In the drawings:

FIG. 1A shows an example of a conventional collimated light sourcelighting technique.

FIG. 1B is a diagram of a conventional fingerprint scanner having acollimated illumination system.

FIG. 2 is a diagram of a conventional fingerprint scanner having adiffuse illumination system.

FIG. 3A is a diagram of a print scanner having a hybridcollimated/diffuse illumination system according to an embodiment of thepresent invention.

FIG. 3B is a diagram that illustrates detection of grey scale shadingwith a print scanner having a hybrid collimated/diffuse illuminationsystem according to an embodiment of the present invention.

FIG. 3C is a diagram that illustrates a hybrid collimated/diffuseillumination system according to another embodiment of the presentinvention.

FIG. 4 is a diagram of an illumination system that includes a lightwedge and diffuse optical elements according to an embodiment of thepresent invention.

FIG. 5 is a diagram that illustrates diffuse light rays reflected from asurface of a light wedge in the illumination system of FIG. 4.

FIGS. 6A, 6B, and 6C illustrate embodiments of a nonuniform illuminationsource array according to a further feature of the present invention.

FIG. 6D illustrates an embodiment of a diffuse illumination systemhaving a zone-controlled nonuniform illumination source array and alight wedge according to an embodiment of the present invention.

FIG. 7 is a diagram that illustrates blue/green illumination on a valleyand ridge of a finger according to an embodiment of the presentinvention.

FIG. 8 is a diagram that illustrates blue/green illumination absorbedinto a ridge of a finger according to an embodiment of the presentinvention.

The present invention will now be described with reference to theaccompanying drawings. In the drawings, like reference numbers indicateidentical or functionally similar elements. Additionally, the left-mostdigit(s) of a reference number identifies the drawing in which thereference number first appears.

DETAILED DESCRIPTION OF THE INVENTION TABLE OF CONTENTS

-   1. Overview-   2. Terminology-   3. Hybrid Collimated/Diffuse Illumination System-   4. Illumination System Having a Light Wedge-   5. Non-Uniform Illumination Source and Control-   6. Blue/Green Illumination-   7. Conclusion

While the present invention is described herein with reference toillustrative embodiments for particular applications, it should beunderstood that the invention is not limited thereto. Those skilled inthe art with access to the teachings provided herein will recognizeadditional modifications, applications, and embodiments within the scopethereof and additional fields in which the present invention would be ofsignificant utility.

1. Overview

The present invention provides illumination for any type of printscanner, including, but not limited to, any type of fingerprint and/orpalm print scanner.

2. Terminology

To more clearly delineate the present invention, an effort is madethroughout the specification to adhere to the following term definitionsconsistently.

The term “finger” refers to any digit on a hand including, but notlimited to, a thumb, an index finger, middle finger, ring finger, or apinky finger.

The term “live scan” refers to a scan of any type of fingerprint and/orpalm print image made by a print scanner. A live scan can include, butis not limited to, a scan of a finger, a finger roll, a flat finger,slap print of four fingers, thumb print, palm print, or a combination offingers, such as, sets of fingers and/or thumbs from one or more handsor one or more palms disposed on a platen.

In a live scan, one or more fingers or palms from either a left hand ora right hand or both hands are placed on a platen of a scanner.Different types of print images are detected depending upon a particularapplication. For example, a flat print consists of a fingerprint imageof a digit (finger or thumb) pressed flat against the platen. A rollprint consists of an image of a digit (finger or thumb) made while thedigit (finger or thumb) is rolled from one side of the digit to anotherside of the digit over the surface of the platen. A slap print consistsof an image of four flat fingers pressed flat against the platen. A palmprint involves pressing all or part of a palm upon the platen. A platencan be movable or stationary depending upon the particular type ofscanner and the type of print being captured by the scanner.

The terms “biometric imaging system”, “scanner”, “live scanner”, “liveprint scanner”, “fingerprint scanner” and “print scanner” are usedinterchangeably, and refer to any type of scanner which can obtain animage of all or part of one or more fingers and/or palm in a live scan.The obtained images can be combined in any format including, but notlimited to, an FBI, state, or international tenprint format.

The term “platen” refers to a component that includes an imaging surfaceupon which at least one finger is placed during a live scan. A platencan include, but is not limited to, a surface of an optical prism, setof prisms, or set of micro-prisms, or a surface of a silicone layer orother element disposed in optical contact with a surface of an opticalprism, set of prisms, or set of micro-prisms.

The term “collimated, diffuse light” refers to light having rays whichhave passed through at least one diffuser and a collimating lens. Suchcollimated, diffuse light can include, but is not limited to, first andsecond portions wherein the first portion of collimated, diffuse lightfalls on a platen as collimated light and a second portion ofcollimated, diffuse light falls on the platen as diffuse light.

3. Hybrid Collimated/Diffuse Illumination System

FIG. 3A is a diagram of a live print scanner 300 having a hybridcollimated/diffuse illumination system 302 according to an embodiment ofthe present invention. Live print scanner 300 detects images of a fingerand/or palm placed on a platen. A platen is any surface on which afinger or palm is placed in print scanner 300. In the embodiment shownin FIG. 3A, the platen 342 is the top surface of prism 340 or any othersurface that receives illumination from the top of the prism 340. Forexample, platen 342 can be a silicone layer or other protective layer orelement provided on top of or in optical contact with prism 340.

Light from hybrid collimated/diffuse illumination system 302 illuminatesplaten 342. When a finger is placed on platen 342, an imagerepresentative of a fingerprint is then reflected from platen 342through prism 340 for subsequent detection by one or more cameras. Inone example, light reflects from platen 342, exits prism 340, and isfocused by imaging lens 350 along an optical axis OA to an aperture 360.Light then passes from aperture 360 to an imaging lens 370 for detectionat a focal plane/sensor plane 380. One or more cameras (not shown) canbe disposed at focal plane/sensor plane 380 to detect and capture theimage of a print. This illumination is described further below withrespect to FIG. 3B.

As shown in FIG. 3A, hybrid collimated/diffuse illumination system 302includes an illumination source array 310, a diffuser 320, a holographicdiffuser 325, and a collimating lens 330 disposed along an optical axis.Illumination source array 310 can be any area light source including,but not limited to, an array of discrete light emitters, such as, lightemitting diodes (LEDs). In one embodiment, the illumination source array310 comprises an array of emitters which are evenly spaced. In anotherembodiment, according to a further feature of the invention,illumination source array 310 comprises an array of emitters which arenot spaced uniformly. For example, illumination source array 310 can bea non-uniform illumination source array as described with respect toFIGS. 6A-6D below according to a further feature of the invention.

Illumination source array 310 can emit light at a single wavelength ornarrowband range of wavelengths, such as infrared, visible, and/orultraviolet wavelengths. According to one further feature of theinvention, illumination source array 310 emits light having a blue/greenwavelength (“blue/green light”) as described further below with respectto an embodiment in FIGS. 7 and 8.

At least part of the light from illumination source array 310 passesthrough diffuser 320 and holographic diffuser 325 to collimating lens330. Diffuser 320 and holographic diffuser 325 each act to diffuse lightemitted from the different individual emitter sources in an array 310.In this way, uniform diffuse illumination is input to collimating lens330. A portion of the diffuse light is then collimated by collimatinglens 330 and passes along the optical axis to prism 340 and platen 342.The remaining diffuse light passed from collimating lens 330 falls onthe platen as diffuse light.

Several advantages are achieved by a hybrid diffuse/collimatedillumination system according to the present invention. The firstportion of the diffuse light collimated by collimating lens 330 whichpasses along the optical axis to prism 340 and platen 342 is efficientlytransmitted from collimating lens 330 through aperture 360 to focalplane/sensor plane 380. The presence of collimating lens 330 achieves amore efficient transfer of optical power through a telecentric printscanner than a diffuse only light source, and reduces the powerrequirements which are needed at illumination source array 310 byapproximately two-thirds. The remaining diffuse light passed fromcollimating lens 330 falls on the platen as diffuse light. Such diffuselight acts as fill light and allows grey scale shading of a print to bedetected by an image sensor.

FIG. 3B illustrates how such advantages are achieved in the operation ofa hybrid diffuse/collimated illumination system according to the presentinvention. Illumination source array 310 is placed at a distance equalto or less than the focal length of collimating lens 330. In FIG. 3B,array 310 is shown between a focal point FP of the collimating lens 330and the lens 330 itself. At least a part (or portion) of the lightemitted by illumination source array 310 will pass through diffuser 320(not shown) and diffuser 325. Each diffuser 302, 325 acts to randomizethe light so that rays travel in many different directions. Only a fewrays 311, 312 of the diffuse light are actually shown in FIG. 3B forclarity. Collimating lens 330 receives all or part of the diffuse lightrays 312 from diffuser 325. A first portion of the diffuse lightindicated by rays 314 is collimated by collimating lens 330 and sent inparallel toward prism 340. This first portion of rays 314 generallycorresponds to that portion of rays 312 traveling as if they originatedwithin a cone at focal point FP. The remaining portion of diffuse lightindicated by rays 316 that passes through collimating lens 330 falls onthe platen as diffuse light. Such diffuse light acts as fill light andallows grey scale shading of a print to be detected by an image sensor.

FIG. 3B further illustrates how a grey scale shaded image of a finger orpalm illuminated by rays 314, 316 is obtained. Only one ridge betweentwo valleys is illustrated and enlarged for clarity. The figure isillustrative and is not an actual ray trace drawn to scale. The totalillumination (that is rays 314, 316) incident upon platen 342 arrivesfrom a number of different directions. Ridges act to absorb rays atcertain incident angles, while valleys act to reflect rays at certainincident angles. The actual angles at which absorption or reflectionoccurs depends upon, among other things, the indices of refraction ofthe ridge, the air at the valley, and the prism and platen. In addition,for some incident angles, diffuse light that falls on the platen surfacepasses through the platen surface and illuminates a valley. Lightreflected from the skin of a ridge at the proper angle, then re-entersthe prism and is transmitted to the sensor plane. This light enhancesthe grey scale range and provides a more desirable image.

Reflected rays 318 at valley regions are detected as “WHITE” regions byan image sensor (shown as regions between points A and B and E and F inFIG. 3B). Ridge regions where no rays are reflected are detected as“Black” regions (shown as a region between points C and D in FIG. 3B).Because of the hybrid illumination of the present invention, reflectedrays 319 at regions at the edge of a ridge are also detected as “GREY”regions with good grey scale shading (shown as regions between points Band C and D and E in FIG. 3B).

In one implementation used with a palm print scanner having a platenapproximately 4 inches by 5 inches, an illumination source array 310 canbe powered by 30 Watts (compared to 100 Watts if diffuse light only wereused) and still provide adequate illumination power. The use of diffuser320 and holographic diffuser 325 randomizes the light emitted fromillumination source array 310 so that cones of light from the discreteemitters are no longer distinguishable, a more uniform illumination areais provided, and the diffuse component of the total illumination allowsgrey scale shading to be detected in the image.

FIG. 3C shows a hybrid collimated/diffuse illumination system 304according to a further embodiment of the present invention. Hybridcollimated/diffuse illumination system 304 includes an illuminationsource array 310, diffuser 320, mirror 322, holographic diffuser 325 andcollimating lens 330. The presence of mirror 322 provides a more compactarrangement for the hybrid collimated/diffuse illumination system 304.Light travels along an optical axis from illumination source 310 throughdiffuser 320 to mirror 322. Mirror 322 then reflects the light along theoptical axis to holographic diffuser 325. A portion of the diffuse lightis then collimated by collimating lens 330 and passes along the opticalaxis to prism 340 and platen 342, while the remaining diffuse lightpasses through collimating lens 330 and falls on the platen as diffuselight.

Hybrid collimated/diffuse illumination systems 302, 304 are illustrativeand not intended to limit the present invention. Diffuser 320 can be anytype of diffuser (e.g., glass, plastic, or holographic). Similarly,diffuser 325 can be any type of diffuser including, but not limited to,a holographic type of diffuser. In one implementation shown in FIGS.3A-3C, a holographic diffuser 325 is used because it is very efficient,and a glass or plastic diffuser 320 is used because it is lessexpensive.

In general, one or more diffusers of any type may be used in hybridcollimated/diffuse illumination systems 302, 304 according to thepresent invention. Accordingly, diffuser 320 or diffuser 325 may beomitted or additional diffusers may be added. Diffuser 320 has anadvantage in that it is located at or near the array of discrete emittersources thereby making the illumination more uniform near theillumination source. Diffuser 325 is provided near the collimating lens330 to further ensure that uniform illumination is input to collimatinglens 330. Collimating lens 330 is provided near prism 340 to ensure atleast part of the diffuse light is collimated and efficiently passed toprism 340 and through to focal plane/sensor plane 380. These locationsare illustrative. Diffuser 320 and/or diffuser 325 and collimating lens330 may each be located at different relative locations depending on aparticular application or configuration.

Hybrid collimated/diffuse illumination systems 302, 304 can be used withany type of optical fingerprint and/or palm print scanner including, butnot limited to, a single finger scanner, multiple finger scanner, palmprint scanner, rolled finger print scanner, and/or a slap fingerprintscanner.

4. Illumination System having a Light Wedge

FIGS. 4 and 5 illustrate a further embodiment of the present invention.FIG. 4 is a diagram of an illumination system 400 in a print scannerhaving a light wedge 420. An illumination source array 310 inputs lightat a end region 426 of light wedge 420. Light is internally reflectedwithin light wedge 420 and passes to a reflector/diffuser surface 422.Reflector/diffuser surface 422 is one angled face or surface of lightwedge 420. Preferably, surface 422 is provided at an angle with respectto the optical axis along which light is emitted by illumination source310. In one embodiment, reflector/diffuse surface 422 acts to bothreflect light and make the reflected light more diffuse. As shown inFIG. 5, light rays 500 emitted by illumination source 310 pass throughlight wedge 420 to impinge on reflector/diffuser surface 422. Diffuse,reflected rays 510 then pass from surface 422 out through the surface424 of light wedge 420. For clarity, other ray paths illustrating theinternal reflection of light within light wedge 420 are omitted. Thisinternal reflection within light wedge 420 provides a further advantage,however, as it tends to make the light even more diffuse and improvegrey scale shading.

As shown in FIG. 4, light passing from surface 424 or light wedge 420then passes to diffuser 430. Diffuser 430 makes the light even morediffuse so that uniform illumination is provided to platen 342. When afinger is placed on platen 342 as shown in FIG. 4, an image of thefinger is then sent through optical system 440 to camera system 450 fordetection and processing. Optical system 440 can be any conventionaloptical system in a print scanner. Similarly, camera system 450 can beany type of camera including, but not limited to, one or more CCD orCMOS cameras.

In one embodiment, reflector/diffuser surface 422 is a layer of highlyreflecting white paint applied to the surface of a glass light wedge420. The white paint acts as a first diffuser seen by the illuminationlight source array 310. This diffuser acts to remove at least part ofthe illumination structure caused by the one or more cones of lightemitted by the light source array 310. The second diffuser 430 acts toremove more or all of the remaining illumination structure such that auniform illumination is passed to prism 340.

An illumination system having a light wedge according to the presentinvention can be used with any type of illumination light source in anytype of print scanner. For instance, illumination system 400 having alight wedge 420 can be used with any type of optical fingerprint and/orpalm print scanner including, but not limited to, a single fingerscanner, multiple finger scanner, palm print scanner, rolled fingerprint scanner, and/or a slap fingerprint scanner. As described above,illumination source array 310 can be any area light source including,but not limited to, an array of discrete light emitters, such as, lightemitting diodes (LEDs) or laser diodes. In one embodiment, theillumination source array 310 comprises an array of emitters which areevenly spaced. In another embodiment, according to a further feature ofthe invention, illumination source array 310 comprises an array ofemitters which are not spaced uniformly. For example, illuminationsource array 310 can be a non-uniform illumination source array asdescribed with respect to FIGS. 6A-6D below according to a furtherfeature of the invention.

Illumination source array 310 can emit light at a single wavelength ornarrowband range of wavelengths, such as infrared and/or visiblewavelengths. According to one further feature of the invention,illumination source array 310 emits light having a blue/green wavelength(“blue/green light”) as described further below with respect to anembodiment in FIGS. 7 and 8.

5. Non-Uniform Illumination Source and Control

FIGS. 6A, 6B, 6C, and 6D are diagrams of a non-uniform illuminationsource array according to a further feature of the present invention. Asshown in FIG. 6A, non-uniform illumination source array 600 includes acenter region 610 and perimeter region 612. Non-uniform illuminationsource array 600 is made up of a plurality of discrete emitters such aslight emitting diodes (LEDs). Center region 610 is an area where thedensity of emitters is lower than the density of emitters in theperimeter region 612. In this way, non-uniform illumination source array600 has an advantage in that natural light falloff that occurs in aperimeter region of a telecentric imaging system is corrected by therelatively higher density of emitters arranged in the perimeter region612. In addition, according to a further feature, each emitter can beindividually controlled to correct for or minimize drift and maximizeflexibility. This individual control and flexibility further enables adesigner of a print scanner to make sure that uniform, flat illuminationis provided across a platen.

FIG. 6B shows one example according to the present invention. In thisexample, non-uniform illumination source array 600 consists of an arrayof 64 LEDs (D1-D64). Center region 610 is made up of 30 LEDs (D12-D17,D20-D25, D28-D33, D36-D41, and D44-D49). Perimeter region 612 consistsof LEDs D1∝D11, D18-D19, D26-D27, D34-D35, D42-D43, and D50-D64.

FIG. 6C shows a non-uniform illumination source array 620 according toanother embodiment of the present invention. Non-uniform illuminationsource array 620 includes a center region 630, intermediate region 632,and perimeter region 634. In this embodiment, the density of emitters ishighest in perimeter region 634 and lowest in center region 630.Intermediate region 632 has a density of emitters in between that ofcenter region 630 and perimeter region 634. The present invention is notso limited, and additional intermediate regions can be provided tocorrect for natural light falloff as desired.

FIG. 6D illustrates an embodiment of a diffuse illumination systemhaving a zone-controlled non-uniform illumination source array 650 and alight wedge 420 according to an embodiment of the present invention.Zone-controlled non-uniform illumination source array 650 has an arrayof emitters divided into three groups 652, 654, 656. First group 652corresponds to a first zone (zone 1). Second group 654 corresponds to asecond zone (zone 2). Third group 656 corresponds to a third zone (zone3). In one example, group 652 and group 656 each have five emitters,while group 654 has 19 emitters. Emitters in each of groups 652, 654 and656 are individually controlled as respective groups. This simplifiescontrol compared to individually controlling each emitter independentlybut still provides enough flexibility to correct for natural light falloff or drift, so that a flat, uniform illumination of sufficient poweris provided to a platen.

In each of embodiments of FIGS. 6A-6D, current control circuitry (notshown) is coupled to the individual emitters or groups of emitters aswould be apparent to a person skilled in the art given this description.Such circuitry provides appropriate current levels to each emitter orgroups of emitters to correct for natural light fall off or drift, sothat a flat, uniform illumination of sufficient power is provided to aplaten. Such current levels can be set manually or automatically inadvance as part of a calibration routine and/or adjusted in real-timebased on feedback from the detected images.

6. Blue/Green Illumination

In one embodiment, the present invention uses an illumination lightsource emitting light in the blue/green spectrum, that is, a wavelengthor narrowband of wavelengths equal to or approximately equal to 510 nm,to enhance the dynamic range of grey scale shading.

The inventors have compared images of prints obtained using conventionalred light operating at 650 nm and images obtained using blue/green lightat 510 nm. Results obtained by the inventors indicate an approximately14% to 20% increase in the dynamic range of grey scale shading in animage of a print of a finger or palm detected with a print scanner usingblue/green light at about 510 nm. Increasing the dynamic range of greyscale shading in a detected print image further causes the print scannerto operate well over an even wider range of skin conditions (i.e., dry,wet, oily, etc.).

FIG. 7 is a diagram illustrating an illumination scheme for a printcanner 700 highlighting the effect of a blue/green illumination sourceon a valley of a finger according to an embodiment of the presentinvention. Print scanner 700 comprises, inter alia, an illuminationsource 702, a diffuser 704, a prism 706, and a camera 708. A finger 710is placed on a platen. In this example, the platen is a top outsidesurface of prism 706 or any other surface that receives illuminationfrom the top of the prism 706. For example, the platen can be a siliconelayer or other protective layer or element provided on top of or inoptical contact with prism 706.

According to one feature of the present invention, illumination source702 illuminates a blue/green light onto diffuser 704. The blue/greenlight has a wavelength of approximately 510 nm. Diffuser 704 distributesthe illuminated blue/green light evenly through prism 706 onto finger710. The surface of finger 710 is comprised of ridges 712 and valleys714.

When the blue/green light is incident on a platen/ridge interface at avalley 714 of finger 710, the light reflects off the internal surface ofprism 706 and may be directed into camera 708. In other words, wherevalley 714 of finger 710 exists, the blue/green light illuminated fromlight source 702 exhibits total internal reflection. Blue/green lightthat strikes finger valley 714 is totally reflected back into the systemtoward camera 708. In the case of a ridge, blue/green light is absorbedfor light incident on a platen/ridge interface. FIG. 8 shows theblue/green light from illumination source 702 being diffused into prism706 and hitting ridge 712 of finger 710. When the blue/green light hitsridge 712, some of the blue/green light 802 is absorbed into finger 710.The more light absorbed into finger 710 at ridge 712, the higher theimage contrast between ridge 712 and valley 714 for a fingerprintcaptured by camera 708. Camera 708 then detects a high contrast imagerepresentative of the valleys and ridges of a fingerprint of finger 710.For some angles, diffuse light that falls on the platen surface passesthrough the platen surface and illuminates a valley. Light reflectedfrom the skin of a ridge at the proper angle, re-enters the prism and istransmitted to the sensor plane. This light enhances the grey scalerange and provides a more desirable image.

According to further embodiments of the present invention, blue/greenlight is used to illuminate a platen in a print scanner. Such blue/greenlight is less than 650 nm, and is preferably at or near approximately510 nm. Any type of platen and any type of fingerprint and/or palm printscanner can be used. In this way, images having an improved grey scalerange are obtained for prints, including prints of all or part offinger(s) and/or palm(s).

7. Conclusion

While specific embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the invention as definedin the appended claims. Thus, the breadth and scope of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

1. An illumination system that provides illumination for a platen in aprint scanner, comprising: an illumination source array that emits lightfrom a plurality of discrete light sources; and a light wedge having oneend surface that receives light emitted from said illumination sourcearray and a reflective surface that reflects light out of said lightwedge toward the platen, wherein said reflective surface is a diffuse,reflective surface including a roughened surface coated by a layer ofreflective paint, whereby uniform illumination is provided to theplaten.
 2. The illumination system of claim 1, wherein said illuminationsource array comprises a plurality of sources that emit blue/greenlight.
 3. An illumination system that provides illumination for a platenin a print scanner, comprising: an illumination source array that emitslight from a plurality of discrete light sources, wherein said pluralityof sources are divided into at least a center region and a perimeterregion, wherein the density of sources provided in said perimeter regionis greater than in said center region; and a light wedge having one endsurface that receives light emitted from said illumination source arrayand a reflective surface that reflects light out of said light wedgetoward the platen, whereby, uniform illumination is provided to theplaten.
 4. The illumination system of claim 3, wherein the intensity ofeach source can be independently controlled relative to other sourcessuch that a flat, uniform illumination is provided to the platen.
 5. Anillumination system that provides illumination for a platen in a printscanner, comprising: an illumination source array that emits light froma plurality of discrete light sources; and a light wedge having one endsurface that receives light emitted from said illumination source arrayand a reflective surface that reflects light out of said light wedgetoward the platen, wherein said plurality of sources is divided into atleast three groups in at least three respective zones, whereby, theintensity of each group of sources can be independently controlledrelative to other groups such that a flat, uniform illumination isprovided to the platen.
 6. A method for providing efficient, uniformillumination to a platen, comprising: arranging a plurality of discretelight sources into at least a center region and a perimeter region,wherein the density of sources provided in said perimeter region isgreater than in said center region; emitting light from said pluralityof discrete sources; passing the emitted light through a light wedge toobtain diffuse light; and illuminating the platen with the diffuse lightsuch that an image of a print of a finger or palm placed on the platencan be obtained.
 7. The method of claim 6, wherein said emitting stepincludes emitting blue/green light.
 8. The method of claim 6, furthercomprising independently controlling the intensity of each sourcerelative to other sources such that a flat, uniform illumination isprovided to the platen.
 9. A method for providing efficient, uniformillumination to a platen, comprising: arranging a plurality of discretelight sources into at least three groups in at least three respectivezones; emitting light from said plurality of discrete sources; passingthe emitted light through a light wedge to obtain diffuse light;independently controlling the intensity of each group of sourcesrelative to other groups of sources such that a flat, uniformillumination is provided to the platen; and illuminating the platen withthe diffuse light such that an image of a print of a finger or palmplaced on the platen can be obtained.
 10. For use in a print scanner, anillumination method for improving a range of grey scale shading,comprising: emitting light in a blue/green spectrum from a plurality ofdiscrete sources, wherein said plurality of sources are divided into atleast a center region and a perimeter region, wherein the density ofsources provided in said perimeter region is greater than in said centerregion; and illuminating a platen, having an object with a pattern ofridges and valleys thereon, with at least part of the emitted light inthe blue/green spectrum.
 11. The method of claim 10, wherein theblue/green spectrum comprises a single wavelength equal to orapproximately equal to 510 nm or a narrowband of wavelengths thatincludes a wavelength of 510 nm.
 12. The method of claim 10, wherein theintensity of each source can be independently controlled relative toother sources such that a flat, uniform illumination is provided to theplaten.
 13. The method of claim 10, wherein said plurality of sources isdivided into at least three groups in at least three respective zones,whereby the intensity of each group of sources can be independentlycontrolled relative to other groups such that a flat, uniformillumination is provided to the platen.